Resolving spatial heterogeneities in exhumation and surface uplift in Timor-Leste: Constraints on deformation processes in young orogens

Abstract

Although exhumation and surface uplift are important parameters in understanding orogenesis, the opportunity to measure both in close proximity is rare. In Timor-Leste (East Timor), deeply exhumed metamorphic rocks and piggyback deepwater synorogenic basins are only tens of kilometers apart, permitting direct relation of uplift and exhumation by comparing micropaleontology to thermochronology interpreted through one-dimensional thermal modeling. Foraminifera in two deepwater synorogenic basins suggest basin uplift from depths of 1-2 km to depths of 350-1000 m between 3.35 and 1.88 Ma. Thermochronologic sampling was conducted in the central mountain belt between these basins. Of four muscovite 40 Ar/ 39 Ar samples, one provides a reset age of 7.13 ± 0.25 Ma in the Aileu high-grade belt that suggests~9-16 km of exhumation since that time. Eighteen zircon (U-Th)/He samples contain a group of reset ages in the Aileu Complex ranging from 4.4 to 1.5 Ma, which suggest exhumation rates of 1.0-3.1 mm/yr with 2.7-7.8 km of exhumation since these ages. Thirteen apatite (U-Th)/He ages in the Gondwana Sequence range from 5.5 to 1.4 Ma, suggesting 1-2 km of exhumation and defining a pattern of exhumation rates (ranging from 0.2 to 1.3 mm/yr) that positively correlates with average annual rainfall. Seven apatite fission track samples display varying degrees of partial resetting, with greatest resetting where apatite (U-Th)/He ages are youngest. Together, these data demonstrate extreme variability in surface uplift and exhumation over small spatial scales. We propose ongoing subsurface duplexing driven by subduction and underplating of Australian continental crust as the predominant driver for surface uplift and uplift-induced exhumation.

Untangling inconsistent magnetic polarity records through an integrated rock magnetic analysis: A case study on Neogene sections in East Timor

“…The island of Timor has been subjected to folding, thrusting, and uplift since ∼10 Ma [ Harris , ; Haig and McCartain , ; Spakman and Hall , ; Fichtner et al ., ; Audley‐Charles , ] [ Tate et al ., ] as a result of collision of overriding Banda oceanic lithosphere and overlying volcanic arc with the subducting continental margin of NW Australia. The downgoing Australian continental margin's upper crust contains two major sequences separated by a décollement horizon [ Carter et al ., ; Harris , ; Audley‐Charles , ] (Figure a): first, a Paleozoic‐lower Mesozoic Gondwana “prerift to synrift” sequence (Gondwana megasequence) [ Carter et al ., ] that formed prior to and during Jurassic extension along the northern Australian margin.…”

“…The studied sediments were deposited in synorogenic piggyback basins that occur in and occur in places where neither the Banda terrane nor the Australian Continental Margin sequence is present on this décollement. These sequences are filled with deep‐marine (>2000 m) limestones at the base [ Audley‐Charles , ; De Smet et al ., ; Haig and McCartain , ; Roosmawati and Harris , ; Haig , ; Tate et al , ] passing upward into pelagic marl and turbidite deposits [ Haig and McCartain , ; Nguyen et al ., ]. These sediments form the Viqueque Formation and are presently found across the southern half of the island.…”

“…The country of East Timor is highlighted. Modified from Tate et al []. (b) Simplified geological map of Timor (modified from Standley and Harris [] and Audley‐Charles []) with the locations of the two sampled sections in the Viqueque formation.…”

“…In this paper, we report on paleomagnetic results obtained from an uppermost Miocene‐Pliocene deep‐marine sedimentary sequence [ Haig et al ., 2012; Nguyen et al ., ] on the island of Timor in the Malay Archipelago. Two sedimentary sections were sampled for a biomagnetostratigraphic study aimed to establish uplift rates of the young Timor orogeny [ Tate et al , ]. We will show that among the dominant magnetic carriers are greigite and magnetite, and that a classic paleomagnetic directional analysis of these sections yields magnetic polarity patterns that are grossly inconsistent with biostratigraphic constraints.…”

Unraveling the roles of asymmetric uplift, normal faulting and groundwater flow to drainage rearrangement in an emerging karstic landscape

“…In western Sumba, Miocene units consist in carbonate platform deposits that evolve laterally into deep basin facies deposits in eastern Sumba (Von der Borch et al, 1983;Van der Werff et al, 1994). Subduction of thick buoyant continental Australian crust under the Banda arc started during the Late Miocene and induced uplift and emergence of the Sumba ridge (Harris, 1991;Fortuin et al, 1997;Hall and Smyth, 2008;Haig, 2012;Tate et al, 2014). Ensuing uplift is responsible for (1) the diachronic emergence of Sumba starting 3 Ma ago (Roep and Fortuin, 1996) in the east, and~1 Ma ago at Cape Laundi (Pirazzoli et al, 1993), (2) the formation of a staircase sequence of Quaternary coral reef terraces along the northern flank of the island, and (3) coeval south-verging collapse of the southern flank of the island (Fleury et al, 2009) (Figure 1B).…”